/// <summary>
/// Removes a queued frame from the output FIFO and transmits it.
/// </summary>
void EmptySendFifo()
{
var frame = sendFifo.Dequeue();
WriteMac("Outputting an Ethernet frame for " + frame.Destination + ".");
emptyingFifo = true;
// Serialize the Ethernet frame object into a sequence of bytes.
var frameBytes = frame.Serialize();
// Call into the physical layer to put the bytes "on the wire".
Transmit(frameBytes);
}
/// <summary>
/// Processes the queue of incoming IP packets.
/// </summary>
void ProcessPackets()
{
try {
var tuple = inputQueue.Dequeue();
var packet = tuple.Item1;
var ifc = tuple.Item2;
packet.TimeToLive--;
// Drop packet and send "TTL Expired"-ICMP back to packet originator.
if (packet.TimeToLive == 0)
{
if (packet.Protocol != IpProtocol.Icmp)
{
SendIcmp(ifc, packet.Source, IcmpPacket.TimeExceeded(packet));
}
return;
}
// Incrementally update the checksum.
var sum = (uint)(packet.Checksum + 0x01);
packet.Checksum = (ushort)(sum + (sum >> 16));
if (IsPacketForUs(packet))
{
// See if we have all parts and can reassemble the original packet.
if (IsFragment(packet))
{
ReassemblePacket(packet);
}
else
{
// If it's not a fragment, hand the data up to the transport layer.
HandUp(packet.Data, packet.Protocol);
}
}
else
{
// If it's not for us, see if we can forward it to its destination.
RoutePacket(packet, ifc);
}
} finally {
// Nodal processing delay is the time it takes on average to process
// a single IP packet.
if (inputQueue.Count > 0)
{
Simulation.Callback(nodalProcessingDelay, ProcessPackets);
}
}
}
